1. GPS data during SOP1 & SOP2 (D4B2) Olivier Bock, LAREG IGN Pierre Bosser, ENSG IGN Contributions from: -C. Champollion, E. Doerflinger (LDL) France -R. Pacione (E-GEOS/ASI) Italy -J. A. Sanchez Sobrino (IGN-E), A. Seco (UPN), A. Botas (Logica), C. Sanchez Tugores (Sitibsa), L. García Pellicer (ARAGEA), Spain -M. Vasconcelos (DGT), Portugal -J. Jones, D. Offiler (UKMO), UK 1 IODAMED meeting, 16 May 2014

2. The operational GPS network and ZTD data flow (EGVAP -> assimilation in NWP models) A reprocessed dataset for HYMEX SOP1+2 – Screening of ZTD data – Conversion of ZTD to IWV – Comparison of GPS IWV to AROME WMED Op An IODAMED meeting, 16 May 20142 Outline

3. E-GVAP EUMETNET EIG GPS Water Vapour Program Aim: use NRT GNSS ZTD for operational meteorology. EGVAP is a consortium of 13 National Weather Services working in close collaboration with 11 National Mapping Agencies. GNSS network is composed of public & private stations and counts ~ 1500 sites. GNSS rinex data are processed by 15 ACs in Near Real Time (NRT), i.e. latency < 1h45min. NRT ZTD disseminated by UMKO on the GTS (BUFR files) and assimilated in NWP models by UKMO, Meteo-France, DMI… May 2012 3 IODAMED meeting, 16 May 2014

4. 4 ZTD GPS data input AROME - France 10 000 values per 3h 15 GPS ACs with different sofware and processing procedures => ZTD dataset is inhomogeneous

5. IODAMED meeting, 16 May 20145 NRT_EGVAP_SGN (IGN/SGN, France) Network: - RGP (France) + reference stations (321 sites) Processing: -Bernese GPS software -Ultra-rapid IGS orbits, fixed positions, CO=10°, no gradients, ZTD values at HH+00, 15, 30, 45, 59’ NRT_EGVAP_IGE (IGN, Spain) Network: - Spain + Portugal + reference stations (288 sites) Processing: -Bernese GPS software -Ultra-rapid IGS orbits, ZTD values: HH+00, 15, 30, 45, 59’ NRT_EGVAP_ASI + NRT_EGVAP_ASI1 (E-GEOS/ASI, Italy) Network: - Italy + reference stations (164 sites) Processing: -GIPSY-OASIS II software -Ultra-rapid JPL orbits, fixed positions, ZTD values HH+00, 15, 30, 45’ NRT ZTD data archived on hymex DB

6. IODAMED meeting, 16 May 20146 sedoo.fr Hymex database

7. IODAMED meeting, 16 May 20147 Comparison of NRT ZTD data at common sites ASI – SGN, 44 common sites, different software Mean = -3 ± 5 mmStd. = 7 mm IGE – SGN, 50 common sites, same software Mean = 0 ± 2 mm Std. = 7 mm

8. IODAMED meeting, 16 May 20148 Reprocessed network EGVAP REPRO 773 stations (3 Analysis Centres) 970 stations (2 ACs, 21 networks) Sardinia HYMEX_DE HYMEX_FR Orphéon 15 networks IGE SGN ASI

9. IODAMED meeting, 16 May 20149 Reprocessing by IGN/LAREG, France Network: 823 sites -France : RGP (349 sites) + Orphéon (182 sites) -Temporary sites : Cévennes (8 sites, Géosci. Montpellier) and Corsica (5 sites, GFZ) -Spain: 14 regions (231 sites) + IGE national network (37 sites) -Portugal: RENEP (43 sites) -North Africa: UNAVCO (5 sites) Processing: -GIPSY-OASIS II software -Final JPL orbits & clocks, ZTD + gradients every 5’, VMF1, 30 h session Reprocessing by e-GEOS/ASI, Italy Network: -Italy: ASI1 + new stations (Sardinia) = 147 sites Processing: -Idem repro_LAREG Reprocessed network Homogenous reprocessing of 970 sites for period 1 Sep 2012 – 31 Mar 2013

10. IODAMED meeting, 16 May 201410 Comparison of NRT to post-proc. data Mean = 0.5 ± 3 mm Std. = 8 mm Mean = -0.1 ± 2 mm Std. = 6 mm Mean = 0.8 ± 2 mm Std. = 4 mm IGE SGN ASI

11. IODAMED meeting, 16 May 201411 Screening of ZTD data 1st step Analysis of formal error for ZTD, station height, and other processing output information 1 – 99 percentiles of ZTD formal error 2nd step Comparison of GPS ZTD data to ZTD data from a NWP model, rejection of data at ± 3  Before After mean Std.dev.

12. IODAMED meeting, 16 May 201412 Conversion of ZTD to IWV accurate to 0.06% accurate to 0.006% Surface pressure or NWP Analysis accurate to 0.1-1 hPa (0.01-0.1%) accurate to 10 -3 m s- 2 (0.01%) accurate to 2.4 % accurate to ±3 % but k’ 2 = 0.047 * k 3 /T m Empirical model Tm = f(Ts) or NWP Analysis T m = 250 ± 20 K (8% variations) Principle: IWV=K(T m )* ( ZTD – ZHD ) Requires auxiliairy data

13. GPS IWV uncertainty: bias ≈ 0.2-0.8 kg/m 2 random ≈ 0.2-1.5 kg/m 2 ZTD uncertainty + ZHD uncertainty + K(T m ) uncertainty 4-6 mm (IGS solution) 0.6-0.9 kg/m 2 1 mm (0.06% k 1 error) + 1-2 mm (0.5-1 hPa Ps measurement error) + 1-2 mm (interpolation error) 0.3-0.5 kg/m 2 1-2% (k 2 & k 3 error) + 1-2% (T m error < 5K) 0.1-1.1 kg/m 2 IWV=5 kg/m 2 IWV=40 kg/m 2 Uncertainty budget of GPS IWV

14. IODAMED meeting, 16 May 201414 Comparison of GPS IWV to AROME WMED Mean = 1.5 kg m -2 Std.= 1.5 kg m -2 Slope = 0.96 Correl = 0.92 16 networks, 1 month (Sep 2012) Auxiliairy data for IWV conversion: AROME WMED (surf + T) + emp. model Tm =f(Ts)

15. Finalise validation of reprocessed GPS ZTD dataset – ZTD data screening (improve method, 1st step) – ZTD to IWV conversion (assess auxiliairay datasets) – Validate GPS IWV data by comparison with other data (MWR…) Assimilation of reprocessed GPS ZTD data – AROME WMED reanalysis Prepare data (BUFR files) and assimilation system Test impact of assimilation, case studies – Assimilation in research models Monitoring of radiosonde humidity biases Validation of simulations (case studies) Process studies (HPE) IODAMED meeting, 16 May 201415 Next steps